The present invention relates to a gearbox or gearbox assembly used with deep oil well pumps and more particularly to a gearbox or gearbox assembly for a deep oil well pump, where the gearbox, motor and pump are all disposed within the drilled hole of the well.
In deep oil well production it is necessary to pump the natural oil from within the earth to the surface. In one method, an eccentric worm pump is located in the borehole at the desired depth and the drive and motor are located on the surface. Drives for eccentric worm pumps for the transportation of liquids in the natural oil conveying industry are known, in which a motor drives a pump down in a well by means of deep well pump rods at a speed which is constant, can be switched in phases or infinitely (e.g., electrically, mechanically or hydrostatically controlled) via a step-down gear all of which is positioned above ground. The deep well pump rods, however, are long, heavy, expensive and power-consuming rods. Such drives and the rods also are unsuited for use with deviated wells. Further, such drives cannot be adapted for use at the bottom of the well or in the borehole due to their large dimensions.
Attempts have been made to develop a gearbox assembly that can be co-located in the borehole along with the pump and motor. However, these gearboxes were unable to sustain operational capability for long periods of time under the severe environmental conditions, high temperatures on the order of 120-130xc2x0 C. (250-270xc2x0 F.) and high pressures on the order of 40-50 atmospheres. Such gearbox assemblies also proved to be very complex and employed multiple lubrication systems.
It thus would be desirable to provide a gearbox that can resist the environmental conditions that exist with deep oil wells, that would develop high torque and which would be small in cross section so it could be located with the pump and motor in the well borehole. It would be particularly desirable to provide such a gearbox that would be capable of withstanding the high axial loads developed by the head of pumped oil. It also would be desirable to provide such a gearbox that would operate for long time periods and include an improved lubrication system that would ensure adequate lubrication and cooling of rotating and bearing components of the gearbox when located in a borehole in comparison to prior art devices.
The present invention features a gearbox that is used to interconnect an electric motor to a deep oil well tube pump such as an eccentric worm pump. The gearbox of the present invention creates a relatively maintenance-free gear unit that permits large torques, tolerates large axial forces on the drive shaft and is built so small that it can be used in a very deep well without problems as experienced by prior art units. Also, such a gearbox can withstand the environmental conditions in oil wells at depths of 800-1500 meters while achieving a high service life, on the order of a year, in comparison to prior art gearboxes.
In one aspect of the present invention, the gearbox includes a drive shaft that is mechanically interconnected to a pump, a reduction gear assembly that is mechanically interconnected to the drive shaft and an electric drive motor, a bearing system that axially and radially supports rotating members of the reduction gear assembly, a lubrication system and a compensator that is fluidly coupled to the lubrication system.
The lubrication system provides a lubricating fluid to the bearing system and the gear reduction assembly for lubrication and cooling. The compensator includes a reservoir of cooled lubricating fluid for the lubrication system. The compensator also provides pressure compensation between the pressure external to the gearbox and the lubrication system and the internal pressure of the lubrication system. In this way, volumetric expansion or contraction of the fluid comprising the lubrication system is accommodated. This minimizes the potential for fluid leakage from the lubrication system or rupture of the lubrication system pressure boundary during a volumetric expansion or an influx of contaminants during a volumetric contraction. Additionally, the compensator functions as a heat exchanger so as to cool the lubricating fluid in the reservoir.
In a specific embodiment, the lubricating system further includes a channel system fluidly coupled to the compensator and the reservoir thereof and a pump spindle that is fluidly coupled to the channel system. The pump spindle also is mechanically interconnected to a portion of the reduction gear assembly so the pump spindle is rotated thereby. The rotation of the pump spindle causes the lubricating fluid to flow through the channel system and the compensator thereby lubricating and cooling the bearing system and the gear reduction assembly.
In another aspect of the invention, the reduction gear assembly includes one or more stages of planetary gearing, wherein one stage of gearing, the final planet stage, includes three or more planet wheels, a pinion cage and a pinion cage member. The pinion cage member is mechanically interconnected to both of the pinion cage and the drive shaft. The three or more planet wheels and the pinion cage are rotatably interconnected so rotation of the planet wheels causes the pinion cage and the pinion cage member to rotate about a common axis.
In specific embodiment, the reduction gear assembly further comprises two stages of planetary gearing, a first planet stage and the final planet stage, where the final planet stage further includes five planet wheels and a sun wheel that rotatably engages each of the five planet wheels. In this way, rotation of the final planet stage sun wheel causes the planet wheels to rotate thereabout and thus cause the pinion cage and pinion cage member to rotate about the common axis responsive to the rotation of the final planet stage sun wheel.
The first planet stage includes a stationary pinion cage; three or more planet wheels, more particularly three planet wheels, that are each rotatably secured to the stationary pinion cage and a hollow wheel. The hollow wheel is disposed about the three or more planet wheels and is mechanically interconnected to each of the planet wheels so rotation of the planet wheels causes the hollow wheel in turn to rotate. In this way, the first planet stage sun wheel, which is mechanically interconnected to the drive motor and the three or more planet wheels, causes the hollow wheel to rotate. Also, the first planet stage hollow wheel supports the final planet stage sun wheel so rotation of the first stage hollow wheel causes the final planet stage sun wheel to rotate.
In a more specific embodiment, the gearbox further comprises a housing in which is disposed the reduction gear assembly, the bearing system, the compensator and the lubricating system. The housing also includes an internal tooth system cut into the housing and disposed so as to engage teeth of each of the planet wheels of the final planet stage. In this way, each of the planet wheels of the final planet stage rotate about the final planet stage sun wheel.
Making use of the entire construction area available in the final planet phase (diameter) is a great advantage, meaning that a maximum driven end torque can be achieved with the best possible service life by optimizing the gear-tooth system of this phase and a favorable selection of the number of planet pinions. A further advantage is also to be seen in the existence of pressure compensation between the oil space and the outer wall of the gear.
In another aspect of the invention, the bearing system includes a bearing subassembly for supporting the final planet stage, the bearing sub-assembly including a plurality of axial and radial bearings. More specifically, the bearing sub-assembly includes a radial bearing, a spring-loaded small axial bearing and one or more thrust roller bearings such as one or more tapered roller bearings or axial cylinder roller bearings. The radial bearing and spring loaded axial bearing are disposed about and on one side of the final planet stage pinion cage member and provide axial and radial support for the final planet stage pinion cage member. The one or more thrust roller bearings are disposed about and on one side of the final planet stage pinion cage and provide axial and radial support for the final planet stage pinion cage. In specific embodiments, the one or more thrust roller bearings are preloaded by the spring-loaded small axial bearing so as to avoid lifting of the tapered or axial cylinder roller bearings. Also, the one or more tapered or axial cylinder roller bearings can be arranged in one of a tandem or a multiple bearing arrangement about and to one side of the final planet stage pinion cage.
Other aspects and embodiments of the invention are discussed below.